This research proposal addresses an important clinical problem - the accurate guidance of intravascular catheters and simultaneous assessment of vessel wall properties including pathology. The research proposed herein seeks to evaluate the feasibility of utilizing time-domain acoustic reflectometry to guide and position intravascular catheters. Acoustic pulses generated at a proximal end of a catheter would propagate through the catheter and into a blood vessel. Reflections arising from the catheter and the vessel can be measured and analyzed to obtain an acoustic image (cross-sectional area vs. distance) of the vessel to detect: 1) obstructions within the catheter or the blood vessel, and 2) anatomical landmarks to determine the catheter tip position. The "forward-looking" feature of this approach makes it unique, as compared with intravascular ultrasound (IVUS), which only offers information about what is around ("side-looking") the catheter tip. Another objective is to investigate the possibility of employing acoustic impedance measurements to determine the mechanical properties of the arterial wall tissue just beyond the tip of the IV catheter, with the final goal of detecting atherosclerotic plaque acoustically. Computer simulations and in vitro studies will be performed to evaluate the feasibility of this novel acoustic method. The long-term goal of this research is to develop a series of "smart", "do-it-all" catheters that can be used clinically to guide, position, and monitor intravascular catheters, and to characterize the blood vessel wall tissue just beyond the tip of the catheter.